Diesel 101: Nothing But The Facts

It’s enough to make your head spin: CO2, NOx, EURO 6, WLTP, NEDC, RDE, the list goes on and on. Then there are the government regulations, the taxes, the tests... But what does it all mean? Well worry not – we’re here to help. Here’s absolutely everything you need to know about the future of diesel: the emissions, the tests, the new rules, everything. It’ll make you fluent in dieselese, guaranteed!

For years we were told that cars with diesel engines were great, but their reputation seems to have taken a hit recently. What’s the story?

To understand what’s going on, you have to go back to the 1997 Kyoto Protocol, in which diesel cars were promoted, particularly in the EU, as a way to combat climate change. This was due to them emitting less carbon dioxide (CO2) than petrol cars. (CO2, remember, is a harmful greenhouse gas.)

So what’s the problem?

The information about CO2 emissions that we were told back then is still true – it hasn’t changed. Diesel cars really do produce less CO2 than petrol cars – up to 20 percent less. But there has been some controversy around certain manufacturers’ cars recently. This caused negative press coverage that seems to have given some people the impression that all diesels are now somehow the enemy. That’s not true. In fact, it’s much more complicated.

Complicated because it’s not all about CO2? There are NOx emissions and particulates to think about too, right?

Right. But the new wave of modern diesels are good in this department, too. New diesel cars that meet the tough Euro 6 emissions standards use selective catalytic reduction (SCR) to turn the majority of the potentially harmful nitrogen oxides (NOx) from engines into nitrogen and water, which is safe. Diesel particulate filters (DPF) fitted to all new diesels since 2009 catch more than 90 percent of soot particles.

But cars with diesel engines are becoming less popular.

The latest set of figures for new car purchases in the UK does show a decline in sales, but there was a dip in the market as a whole. Diesel cars still accounted for 42 percent of all new cars bought in the UK in 2017 – that’s a big chunk.

They’re more expensive to buy, which probably doesn’t help.

But, for many people, they’re significantly cheaper to run. The consumer bible Which ran some of its own independent tests recently. They showed that, on average, diesel cars were more fuel-efficient and would save around £200 a year. For people who do a lot of their driving on A roads and motorways, or who cover a lot of miles in a year, that figure will be even higher. So diesel is often a better investment in the long term.

In the longer long term, they’re going to be totally banned, though. Aren’t they?

No. It’s true that the UK Air Quality Plan, published in 2017, outlined intentions to ban the sale of all new diesel and petrol cars from 2040, but there was no indication that existing diesel or petrol cars that were on the road before then were at risk.

So… what happens now?

Well, one positive step is a major change to the testing procedures that are used to rate the emissions produced by cars. This is good news because tests – and test results – were what caused all this confusion about diesel in the first place.

How is this going to be better?

The Worldwide Harmonised Light Vehicles Test Procedure (WLTP), is a collection of new methods for testing emissions and fuel consumption in lab conditions. From September 2018, all new cars will have to be tested in this way, and by January 2019, WLTP figures will be the only ones on display in car dealerships. The speeds, phases of driving and temperatures at which measurements are taken are designed to be far closer to real-world conditions. The old tests being replaced have been around since 1970, and a lot has changed since then.

So, new, more accurate tests. And the chance for customers to make informed decisions about what’s right for them.